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    <script>
        // 通过typeof 去判断数据类型
        var a=222;
        console.log(typeof(a));
        var b=null;
        console.log(typeof(b));
        // 通过isNaN进行判断；
        var a="10";
        console.log(isNaN(a));
        var a="hello";
        console.log(isNaN(a));
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